Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $238.74   11.737%   $266.7609   $266.76   $266.75   $266.80  
  Purchase #2 $184.85   4.388%   $192.9612   $192.96   $192.95   $193.00  
  Purchase #3 $161.74   10.427%   $178.6046   $178.60   $178.60   $178.60  
  Purchase #4 $17.73   7.767%   $19.1071   $19.11   $19.10   $19.10  
  Purchase #5 $166.81   11.578%   $186.1233   $186.12   $186.10   $186.10  
  Purchase #6 $242.99   8.721%   $264.1812   $264.18   $264.20   $264.20  
  Purchase #7 $45.32   6.652%   $48.3347   $48.33   $48.35   $48.30  
  7 purchase totals = $1,058.18       $1,156.0730   $1,156.06   $1,156.05   $1,156.10